Intraocular lenses and other ophthalmic devices are used to restore and correct vision. For example, monofocal intraocular lenses may be used to replace the natural lens of an eye that has developed cataracts. The simplest type of monofocal intraocular lens is spherical lens in which both optical surfaces have a spherical profile. More recently, aspheric lenses have been used to enhance the visual acuity of intraocular lenses. Such aspheric lenses may be used to at least partially correct for aberrations that are produced by an opposing spherical surface and/or aberrations produced by the eye itself (e.g., positive spherical aberrations produced by the cornea of most human eyes). Examples of such lens designs are described in U.S. Pat. Nos. 6,609,793 and 7,137,702, which are herein incorporated by reference in their entirety. Lenses may also be configured to correct for chromatic aberrations inherent in most refractive lenses, for example, through the use of diffractive phase plates (e.g., U.S. Pat. Nos. 4,637,697, 5,121,979, and 6,830,332 and U.S. Patent Application Number 2004/0156014 and 2006/0098163, all of which are also herein incorporated by reference in their entirety).
When spherical intraocular lenses are used, a practitioner may, based on pre-operative ocular measurement, select a lens power that would make a subject somewhat myopic, for example choosing a lens power that provides a subject the best MTF performance or the best visual acuity for objects located at the so called “hyperfocal distance”. One advantage of this approach is an increased likelihood that the subject will have spectacle-free vision for at least one distance or range of distances. That is, if the estimated lens power is incorrect and the intraocular lens is too strong—resulting in a myopic condition—then subject will need correction of distant vision, but will have near or intermediate vision without the use of spectacles or contact lenses. Additionally, if the lens power is selected to give the subject the best MTF performance or best visual acuity for objects located at the hyperfocal distance, the subject generally has a larger range of distances over which objects will be reasonably clear, without the use of spectacles or contact lenses. The increased range provided by choosing the lens power based on the hyperfocal distance may be considered as a type of pseudo-accommodation, in that the resulting vision performance over a range of distances resembles the vision provided by the eye's natural lens prior to the onset of presbyopia.
One potential drawback to selecting the optical power of an intraocular lens based on the hyperfocal distance is that visual acuity for nighttime driving may be reduced, since the best lens performance is for objects located at the hyperfocal distance, rather than at optical infinity. However, most of the objects within the field of view under nighttime driving conditions are at optical infinity and are, therefore, slightly defocused. Since the pupil is fully dilated under these conditions, spherical aberrations may further reduce visual acuity. The effects of spherical aberrations may, however, be reduced by using aspheric lens surfaces that are configured to reduce, correct, or compensate for spherical aberrations of the lens and/or cornea.
Regardless of in-focus condition selected (e.g., at optical infinity or at the hyperfocal distance), aspheric lens surfaces serve to provide an improved visual outcome. This is because, as compared to a substantially equivalent spherical lens, aspheric lenses generally provide better visual acuity or MTF performance at all distances, and not simply at the distance corresponding to the best-focus condition. However, while an aspheric lens with a power selected for the hyperfocal distance generally provides better nighttime driving vision than a spherical lens, the visual acuity will still be reduced compared to the performance when the lens power is selected to provide best-focus at optical infinity.
Accordingly, improved monofocal ophthalmic lenses are needed that will provide both increased visual acuity under nighttime driving conditions and, under other lighting conditions, provide the relatively large depth of focus that is possible by selecting a lens power based on a hyperfocal distance.